program main
    implicit none
    real(8) c,rin,rout,v,rave,rdif
    read(*,*)c,rin,rout
    rave=(rout+rin)/2
    rdif=(rout-rin)/2
    v=2*3.1415926535898**2*rave*rdif**2
    write(*,*)v*c
end program main